One balance behind every position
Cross margin is the default on Hyperliquid. The documentation describes it as allowing maximal capital efficiency by sharing collateral between all other cross margin positions: there is one pot, and every cross position draws on it.
It is also where money lands. A deposit is credited first to the address's cross margin balance, and a position opens in cross margin unless isolated margin is chosen for it.
Sharing runs in both directions, and that is the whole trade-off. The unrealized profit of a cross position is automatically available as initial margin for a new one, with nothing to transfer. The unrealized loss of a cross position is just as automatically taken from the collateral that stands behind all the others.
What it changes for liquidation
The test is on the account, not on the position. A cross position is liquidated when the account value, unrealized profit and loss included, is less than the maintenance margin times the total open notional of every cross position.
A backstop liquidation is therefore an account-wide event. The documentation says all of the trader's cross positions and cross margin are transferred to the liquidator, and that a trader holding no isolated position then ends with zero account equity.
One consequence surprises people: the actual liquidation price of a cross position does not depend on the leverage you set. The documentation says a cross position at lower leverage simply uses more collateral. What moves the liquidation price is the collateral standing in the account, not the number in the leverage box.
Because the liquidation test reads the account, a loss on a market you were not watching brings every other cross position closer to liquidation, and a backstop takes them all. If you want a known maximum loss on one trade, isolated margin is the mode that gives it.
What you can take back out
Not the margin in use. The documentation says the initial margin is used by the position and cannot be withdrawn for cross margin positions. Unrealized profit can be withdrawn, but only if what remains is at least 10% of the total notional of every open position and still meets the initial margin requirement: transfer_margin_required = max(initial_margin_required, 0.1 * total_position_value).
Transferring, there, means anything that removes margin other than trading: a withdrawal, a transfer to the spot wallet, an isolated margin transfer. Closing part of a position is trading, and is not bound by that rule.
Across several dexes
With positions on several perp dexes, what cross shares depends on your account abstraction. For a unified account and for portfolio margin, cross positions on dexes with the same collateral all share margin. With the standard abstraction, cross applies only within the assets of one dex.
And cross is not offered everywhere. A dex deployed under HIP-3 has to have cross enabled on an asset by its deployer, which the documentation says is irreversible, and mainnet validators enforce eligibility standards before it can be: observable liquidity, a reliable external oracle source, resilience to price manipulation. HIP-3 dexes also support a no cross mode, which allows isolated margin with removal but no cross at all.
When cross is the simpler choice
- One position at a time. There is nothing to isolate it from, and the whole balance is its margin either way.
- Positions you want to net. A profit on one holds up another without a transfer, and unrealized profit becomes margin for the next entry on its own.
- Hedged positions in one account, where splitting the collateral would make both legs look thinner than the pair really is.
And when it is not the simpler choice: several unrelated positions, a market whose price can gap, or any trade on which you want the loss to stop at a figure you chose. Those are the cases isolated margin exists for.
Which mode the agent uses
The agent's own bound is not the margin mode, it is the account. The measure of 28 September 2026 found that an approved agent key cannot withdraw, send or move funds between balances, so the largest loss it can reach is what the dedicated account holds. A separate account is what caps the damage, in either mode.
Setting a market's leverage and margin mode is among the few actions an agent key may sign. Orders go out cross on markets that allow it, and in isolated on the markets that refuse cross, which many markets deployed under HIP-3 do.